1. Technical Field
The present invention is in the area of mobile wireless voice and data communications. More particularly, it is related to the field of mobile cellular and personal voice and data communications using Code Division Multiple Access (CDMA) techniques.
2. Description of the Related Art
Of late, there is an increasing demand for wireless services. In order to meet this demand in a cost-effective way and at the same time provide a good quality of service for customers, particularly in terms of the call success rate, service providers need to implement effective load distribution mechanisms with pooled resources. As the first step to meeting this goal, many wireless Code Division Multiple Access (CDMA) service providers maintain a pool of carriers (frequencies) spread over multiple co-located (1-1 overlay system of) Base-station Transceiver Subsystems (BTSes) at each cell site and distribute calls originated at any carrier in the system to any other member of the system using some pre-configured call distribution criteria. The criteria are compound functions of carrier capacities (i.e. number of calls they can support based on the available resources) at any time, their thresholds and priorities determining different types of carrier loading such as even, sequential priority, etc., and some customer preferences for the originating carrier and/or band, and so on. Earlier invention, entitled “Multi-Carrier Traffic Allocation Enhancements to reduce access failures and work across bands,” U.S. patent application Publication Ser. No. 2003/0125039, by one of the co-inventors (Abdennaceaur Lachtar) of the present invention, proposes some effective criteria for load distribution of traffic among carriers in either or both the 800 and 1900 MHZ bands. The current invention enhances that solution with a quality measure for simple and effective implementation of the carrier-to-carrier comparison using any or all of the four load distribution criteria proposed therein. It also contributes to the efficiency of the solution by providing some simple and effective convergence criteria that permit early decision making without affecting the end result and an efficient procedure for implementing them.
When a mobile operates in a single band, effective load distribution with a decent call success rate is achieved by setting the call upon the best carrier (as per this quality measure) in that band. However, the problem becomes complicated because calls originating on dual-band mobiles are required to be equitably distributed across bands, that is, between the 800 and 1900 MHz bands, for better load-balancing. This is particularly important because the 1-1 overlay systems in the two bands may not be identically located due to independent cell planning for the two bands based on their respective radio transmission characteristics. Further, the coverage area of an 800 MHz BTS is roughly 3 times that of a 1900 MHz BTS. Thus it is, in general, possible that a mobile in the range of an 1-1 overlay system in one band, could only be covered, irrespective of its position in that range, by multiple spatially disjoint 1-1 overlay systems (also called a non 1-1 overlay system) in the other band. Criticizing a still earlier proposal to solve this problem using temporary channel assignments followed by multi-pilot hard handoffs on grounds of high access rate failures, earlier invention “Multi-Carrier Traffic Allocation Enhancements to reduce access failures and work across bands” by one of the co-inventors (Abdennaceaur Lachtar) of the present invention, proposes a method of redirecting the call to the other band in situations where there is no capacity on any carrier in the band of call origination. However, the load distribution across bands is not effective in this latter method because of the conservative approach to redirect calls to another band only when there is no capacity in the band of call origination.
There is a need for an efficient and efficacious method that distributes wireless traffic equitably across multiple bands without compromising robustness against call failures. Even though traffic distribution across bands is desirable, there is a risk of call failure because of location of the mobile in the vicinity of a BTS group with low capacity in the other band, prompting a need for a call-fail-safe method that is not unreasonably constrained to make decisions to migrate calls across bands.